1. Field of the invention
The present invention relates to a semiconductor laser beam scanning device for combining the laser beams emitted from a plurality of semiconductor lasers into a single laser beam and for scanning the single laser beam.
2. Description of the Prior Art
Light beam scanning devices having light deflectors for deflecting light beams for line scanning are widely used in various apparatus such as scanning recorders or printers, scanning readout apparatus, and the like. Various means for generating the light beams have heretofore been employed in the light beam scanning devices. One of the conventional light beam sources is a semiconductor laser which is smaller in size, less costly, and lower in electric power consumption than gas lasers and other types of lasers. The semiconductor laser is also advantageous in that the emitted laser beam can be modulated directly by varying the drive current.
However, the semiconductor laser has its own shortcoming. Its output power is low. Semiconductor laser sources now commercially available can produce light outputs ranging from 20 to 30 mW, at most, when they are continuously excited. Therefore, the semiconductor laser cannot be employed in light beam scanning devices which require a high-energy light beam to be scanned, such as scanning recorders for recording images on low-sensitivity materials such as drawn materials, typically metal films and amorphous films.
When certain kinds of phosphors are exposed to a radiation such as X-rays, .alpha.-rays, .beta.-rays, .gamma.-rays, cathode-rays or ultra-violet rays, they store a part of the energy of the radiation. Then, when the phosphor which has been exposed to the radiation is exposed to stimulating rays such as visible light, light is emitted by the phosphor in proportion to the stored energy of the radiation. A phosphor exhibiting such properties is referred to as a stimulable phosphor.
As disclosed in Japanese Unexamined Patent Publication Nos. 55(1980)-12429, 55(1980)-116340, 55(1980)-163472, 56(1981)-11395, and 56(1981)104645, for example, it has been proposed to use a stimulable phosphor in a radiation image recording and reproducing system. Specifically, a sheet provided with a layer of the stimulable phosphor (hereinafter referred to as a stimulable phosphor sheet) is first exposed to a radiation passing through an object such as a human body to have a radiation image stored thereon, and is then scanned with stimulating rays such as a laser beam which cause it to emit light in the pattern of the stored image. The light emitted by the stimulable phosphor sheet upon stimulation thereof is photoelectrically detected and converted to an electric image signal, which is processed as desired to reproduce a visible image on a recording medium such as a photographic light-sensitive material or on a display device such as a cathode ray tube (CRT).
It has been proposed to use a light beam scanning device having a semiconductor laser in the above radiation image recording and reproducing system for scanning the stimulable phosphor sheet to read the radiation image information stored on the stimulable phosphor sheet. It is however necessary to illuminate the phosphor with a stimulating ray of a sufficiently high energy in order to enable the stimulable phosphor sheet to emit light in response to exposure to the stimulating rays. Because of the output shortage, the light beam scanning device with the semiconductor laser has been difficult to employ in the radiation image recording and reproducing system for reading the radiation image information from the stimulable phosphor sheet.
One way to produce a scanning light beam of a sufficiently high energy from a semiconductor laser source would be to use a plurality of semiconductor lasers and combine the laser beams emitted from the semiconductor lasers into a single laser beam. The laser beams from the respective semiconductor lasers may be combined together somewhere in the light beam paths leading to a scanning spot, or be combined together on the scanning spot. As well known in the art, the amount of energy of a laser beam emitted from a semiconductor laser varies with time-dependent changes in the characteristics of the semiconductor laser, and also with the ambient temperature and various other factors. Therefore, it would be necessary to control the combined single laser beam for a constant amount of laser beam energy. It has been known to detect the amount of energy of a laser beam with a laser beam energy detector and feed a signal from the detector back to a laser beam energy control circuit for controlling the amount of energy of the emitted laser beam to keep it constant. However, such a conventional laser beam energy control arrangement would be disadvantageous if used with a plurality of semiconductor lasers for generating a single combined laser beam since there would be required as many laser beam energy detectors and control circuits as the number of semiconductor lasers employed, resulting in a large and expensive light beam scanning device.